A symposium is generally a two-hour, three-hour, or four-hour session, with 30 minutes for a break if longer than two hours. The break is required to begin exactly two hours after the start of the symposium (i.e. morning symposia will begin at 8:00 am with a break from 10:00 am to 10:30 am). Individual speaker presentations are generally 30-40 minutes in length. A complete proposal must include the title and brief (800 characters) description of the symposium, the title of each individual presentation, name and affiliation of all presenters, length of each presentation, anticipated expenses (if applicable), and anticipated sponsorship revenue to help pay the expenses.
See the example of the document that symposium presenters should submit for consideration linked above.